1. Field of the Invention
The present disclosure generally relates to safely transferring sensitive materials. More particularly, the disclosure generally relates to systems and methods for facilitating the transfer of sensitive materials such that exposure to, for example, oxidants is reduced.
2. Description of the Relevant Art
Environmentally sensitive samples are typically transferred from an apparatus filled with an inert gas (e.g., a glove box filled with 99.9995% Argon) or from an ultra-high vacuum (UHV) chamber, into a UHV surface analysis chamber of interest. Transferring and loading environmentally sensitive samples from ambient pressure and into a UHV surface analysis chamber requires a transfer interface, applied as a load lock, with four key capabilities. These capabilities include (1) a sequence with inert gas purging, followed by a pump down to high vacuum, (2) pump down mechanism to transition from viscous to molecular flow regimes, (3) sample manipulation, and (4) software to carry out semiautomatic sequences for repeatability.
The sequence of the inert gas purge, followed by a pump down sequence is an important capability of a commercial load lock. This sequence begins with purging the load lock to displace air (mainly water and molecular oxygen to baseline levels), is followed by applying a positive flow of an inert gas for ˜30 minutes, and is further followed by a pump down to UHV conditions. However, current commercial load locks and transfer interfaces do not have a quality control method to ensure a user that the load lock and other components are operating at working specifications, prior to loading samples into a load lock.
To obtain UHV conditions, a mechanism of differential pumping may be used. In general, differential pumping is a technique to generate a large difference in pressure between neighboring vacuum chambers, e.g., a load lock and pump chambers. This pressure difference is produced when these chambers are physically separated by a plate containing a small orifice while the pump chamber is under continuous vacuum pumping and its neighboring load lock chamber is under pressure, e.g., atmospheric pressure. This technique works because molecules in the pump chamber have a long free mean path (>1 meter) and randomly colliding against the chamber's wall. The latter condition is also known as the molecular flow, while molecules in the load lock under high pressure are traveling in a laminar flow.
Turbomolecular pumps have the widest operating pressure range of typical vacuum pumps and capable of crossing over from high vacuum (molecular flow, p<10−4 Torr) to backing vacuum (Laminar flow, p>1 Torr (1.3 mbar)) and back to high vacuum without detrimental changes in pumping speed and/or throughput. The pump down mechanism to transition from a viscous to molecular flow regimes of commercial interfaces or load locks is typically based on a configuration where a turbomolecular (TM) pump is backed by a rough pump (e.g., a mechanical or dry pump). During the rough pumping, starting at atmospheric pressure (viscous flow), the TM is turned off or isolated and the gas load is re-routed directly into the rough pump. When the pressure drops to less than 0.1 Torr, the power of the TM pump is switched on to pump gas at the molecular flow regime. However, this configuration does not prevent additional exposure to oxidants exposure and/or hydrocarbon contamination, which can originate from roughing pumps during the transition from atmospheric pressure (viscous flow) to UHV conditions (molecular flow). Furthermore, currently available commercial load locks do not have a method for controlling the quality or reliability of the sample transfer.
Environmentally sensitive samples may be loaded into a sample transfer capsule for transitioning into and out of the load lock or transfer interface. However, current sample transfer capsules have many design flaws that may prevent a user from obtaining reliable and repeatable results. Current commercial designs lack the ability to evaluate leaks and/or back streaming generated during operation of the roughing pump. The sample transfer capsule may also be exposed to a pressure gap when the method for transitioning from ambient pressure to UHV is inefficient. In some examples, a single sample may be transported during each transfer event. This may lead directly to inter-sample variance, and current designs are not equipped with repeatability and reliability tests. Indeed, no “golden reference” has been developed to reliably evaluate and compare sample oxidation and contamination during the transfer process. The National Institute of Standards and Technology has never tested a method of transport for measurable kinetics of oxidation, and no prior art discloses methods or systems to reliably calibrate samples during differential pumping.